As the art of underwater listening progresses, the equipment is required to detect fainter and fainter sounds at greater and greater distances with more and more directional precision. The art has advanced so that the designer now has available very sensitive hydrophones and sophisticated beam forming techniques. One way to take advantage of these advances is to deploy the hydrophones in a substantially horizontal straight line beneath the surface as far removed as possible from sources of unwanted sounds, or noise.
In the past, an array of hydrophones has been deployed in a straight line beneath the surface by stringing the hydrophones along a cable towed by a surface ship or low flying helicopter with or without an intermediate buoyant "fish" such as a long cylindrical body. Depth has been controlled by adjusting the buoyancy of the array and/or by the use of weights on the cable itself, the whole being supported by surface floats. Such an arrangement, although suitable for many purposes, has the disadvantage of requiring the presence of the ship during operation which is not only expensive and highly visible but which is a source of noise.
It has been proposed to dispense with the ship by suspending one end of the array from a surface float. It has been found, by suitably adjusting the buoyancy of the array and its hydrodynamic characteristics and by terminating the other end of the array with a sea anchor, that such an array can be stretched out into a substantially horizontal straight line provided there is sufficient current at the required depth. However, when the current drops below a critical value, the array will not hold its straightness.
It is a general object of the present invention to provide an improved system for deploying an array of hydrophones.
A more specific object of the invention is to provide an improved system for deploying a series of hydrophones in a quiet environment beneath the surface of the sea in a substantially straight horizontal line.